This invention relates to a mobile communication system including a base station and a mobile station and, in particular, to a call congestion control method of controlling congestion of calls.
For example, a conventional call congestion control method is disclosed in Japanese Unexamined Patent Publication (JP-A) No. 04-373325 (373325/1992).
Referring to FIG. 1, operation of the call congestion control method will be described. In this method, a mobile terminal receives a call regulation signal supplied from a base station and monitors a call regulation value M represented by the call regulation signal to memorize the call regulation value M in a memory.
In FIG. 1, it is assumed that the mobile terminal receives a request signal while it is present within a regulated area under control of call congestion. Judgement is made about whether the request signal is a call setup request or a position registration request (step ST1). If the call setup request is received (No in step ST1), the call regulation value M is read from the memory in the mobile terminal (step ST2). Then, a random number N is generated in the mobile terminal (step ST4). Comparison is made between the call regulation value M and the random number N (step ST5). If the call regulation value M is smaller than the random number N (Yes in the step ST5), the mobile terminal transmits a call setup signal (step ST6). On the other hand, if the call regulation value M is not smaller than the random number N (No in the step ST5), the mobile terminal produces a call setup reject message (steps ST7 and ST8).
The call congestion control method described above, however, is disadvantageous in the following respect.
It is assumed that a last call has been undesiredly ended by squelch interruption resulting from a squelch function. It is noted here that the squelch function is a function of suppressing a noise by automatically inhibiting the operation of an amplifier of a receiver in absence of a signal input. In this event, the mobile terminal as a squelch-end mobile terminal will immediately produce another call setup request with a high probability in order to restart or continue a speech or conversation undesiredly interrupted. If the squelch-end mobile terminal is present within the regulated area, however, the call setup request from the squelch-end mobile terminal may be rejected for a long period of time, like a new call setup request produced by a new mobile terminal. Thus, it is not assured to restart and continue the speech undesiredly interrupted. It is noted here that the new mobile terminal is a terminal at which the last call is normally ended without being interrupted and that the new call setup request is a request independent from the last call.
This is because, in the conventional call congestion control method, any call setup request produced during control of call congestion is similarly dealt with, irrespective of whether the call setup request is produced by the squelch-end mobile terminal or the new mobile terminal. It will be noted here that the new call setup request is produced in case where the last call is normally ended without squelch interruption.
It is therefore an object of this invention to provide a mobile communication system which is capable of carrying out optimum call congestion control adapted to traffic characteristics and which is capable of accepting a call setup request from a mobile terminal in a short time even during control of call congestion if a last call is undesiredly ended by squelch interruption so as to assure continuation of an interrupted speech in the last call.
It is another object of this invention to provide a mobile terminal used in the above-mentioned mobile communication system.
According to this invention, there is provided a mobile communication system including a base station for transmitting a call regulation signal representative of a call regulation value and a plurality of mobile terminals responsive to the call regulation signal from the base station, each of the mobile terminals having a call setup request section for transmitting a call setup signal to the base station in response to a call setup request, wherein each of the mobile terminals comprises a memory which memorizes whether or not a last call end state of a last call at the mobile terminal is a squelch end by squelch interruption and which, in case where the last call end state memorized in the memory is the squelch end, memorizes as a memorized random minimum value a random minimum value having a value greater than that in case where the last call end state memorized in the memory is not the squelch end; and a probability generating section for generating as a call setup request probability one of a plurality of random numbers having values between a specified random minimum value and a random maximum value; the call setup request section of each mobile terminal comprising a first unit responsive to the call setup request for receiving the call regulation signal to detect the call regulation value from the call regulation signal; a second unit responsive to the call setup request for reading the memorized random minimum value from the memory as a readout random minimum value, supplying the probability generating section with the readout random minimum value as the specified random minimum value to make the probability generating section generate the call request probability; and a third unit for transmitting the call setup signal to the base station if the call setup request probability is greater than the call regulation value.
According to this invention, there is also provided a mobile terminal supplied from a base station with a call regulation signal representative of a call regulation value, the mobile terminal having a call setup request section for transmitting a call setup signal to the base station in response to a call setup request, wherein the mobile terminal comprises a memory which memorizes whether or not a last call end state of a last call at the mobile terminal is a squelch end by squelch interruption and which, in case where the last call end state memorized in the memory is the squelch end, memorizes as a memorized random minimum value a random minimum value having a value greater than that in case where the last call end state memorized in the memory is not the squelch end; and a probability generating section for generating as a call setup request probability one of a plurality of random numbers having values between a specified random minimum value and a random maximum value; the call setup request section comprising a first unit responsive to the call setup request for receiving the call regulation signal to detect the call regulation value from the call regulation signal; a second unit responsive to the call setup request for reading the memorized random minimum value from the memory as a readout random minimum value, supplying the probability generating section with the readout random minimum value as the specified random minimum value to make the probability generating section generate the call request probability; and a third unit for transmitting the call setup signal to the base station if the call setup request probability is greater than the call regulation value.